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RHD-negative (RhD-) blood types are less common among Australians today than previously thought, according to the first robust study of national blood type distribution in almost three decades.
Experts say the new findings underscore the increasing challenge of recruiting new O RhD- donors, but also suggest more patients could be safely transfused with RhD-positive (RhD+) red blood cells.
The research from Australian Red Cross Lifeblood, the national blood and blood products supplier, published in the MJA, examined blood group data from almost half a million blood donors in 2019 – around a fifth of whom were first-time donors – as well as more than 1.3 million people who underwent pathology testing at clinics and hospitals across Australia.
Some 85.9% of pathology patients and 83.8% of first-time blood donors were RhD+ in 2019. This compared with 81% of first-time donors in 1993–94, the last time national data on ABO RhD blood group prevalence in Australia were reported.
Transfusion practitioners substantially rely on universal O RhD- red blood cell (RBC) units, and issuing of these units increased from 11.7% to 17.4% between 2010–11 and 2019–20. However, the study found only 6.5% of pathology samples and 8.7% of first-time donors were O RhD- in 2019, down from 9% in 1993–94. Among blood donors overall, 12% were O RhD-, reflecting the active recruitment of O RhD- blood donors.
The authors wrote that their findings were likely to reflect demographic changes in Australia over the past 30 years, especially extensive immigration from South East Asia, India and China, where the prevalence of B and AB blood groups is generally higher.
In 2019, a higher proportion of first-time blood donors were groups B RhD+ (12.4% v 9.3%) or AB RhD+ (3.9% v 2.9%) compared with the overall donor cohort.
“These findings suggest that the proportion of RhD+ blood group donations is increasing at the expense of RhD- RBC units,” the authors wrote.
They suggested blood holdings should be diversified to encompass more RhD+ stock.
“Our findings and other information could encourage transfusion laboratories and practitioners to stock and transfuse more closely matched ABO RhD RBC units,” they wrote.
Professor David Irving, one of the lead researchers, told InSight+ his team was surprised to find that no rigorous data on blood group distribution had been provided since 1993–94.
“Our study showed the proportion of the population that is O- has changed, which goes to show that we currently over-recruit our O- people in the population,” he said.
“We need a broader representation of donors in our donor pool so we can best match the demand from our patients.”
Professor Irving said Lifeblood was working closely with different ethnic communities on culturally appropriate strategies to recruit blood donors.
“There are over 300 different antigens on the surface of red cells, which vary across ethnic groups,” he said.
“If people have conditions where they require chronic transfusions – take for example, sickle cell anaemia, which is more common among African populations – then they are more likely to have a reaction to one of those antigens if the transfusions are not very closely matched.”
In 2021 Lifeblood identified 154 donors with rare blood groups, using state-of-the art genetics to get the best match between a donor and a patient, he added.
Professor Erica Wood, head of the Transfusion Research Unit at Monash University and consultant haematologist at Monash Health, said group O RhD- donors would always be a priority, but added that with increasing numbers of RhD+ people in the community, the overall need for RhD- red cells should stabilise or even decline.
“RhD- blood should be prioritised for people who are in fact RhD- and group O RhD- red cells for the small number of patients who need emergency transfusions when their blood group is unknown,” Professor Wood said.
Professor Wood, who is also President of the International Society of Blood Transfusion, said best practice was to determine a bleeding patient’s blood type as soon as possible in an emergency, so that patients could be switched from O RhD- to a group-matched blood transfusion.
She also said there was evidence to support using group O RhD+ blood up front in bleeding emergencies, particularly in men and older women.
“Most of these people will be RhD+, but if they turn out to be RhD and do make an anti-D antibody, it’s unlikely to be such a major problem for them, unlike for women of childbearing potential where an anti-D antibody can cause serious problems in a future pregnancy,” she said.
Professor Wood said there was always a “fine balance” between blood supply and demand, but that overall, it was “pretty well aligned in Australia”.
“Sometimes if we start transfusing a patient with group O RhD- cells in an emergency before their blood group is known, but don’t have the total number of units available to keep going with O RhD- support – in a small hospital, for instance – we will cross over to transfusing O RhD+ red cells,” Professor Wood said.
“And sometimes, if we have group O red cells getting close to their expiries, the laboratories will issue those to non-group O patients just to make sure that they don’t expire.
“Supplies are very actively managed, with inventory holdings set in consultation with Lifeblood, moving stock around from small hospitals to large hospitals in a network to minimise wastage,” she said, noting red blood cells only have a shelf life of 42 days.
Professor Wood said group AB blood donors were increasingly asked to donate plasma, as AB is the universal plasma type. As a result, fewer AB RBC units were being issued to hospitals.
“Hospitals are often reluctant to stock many B and especially AB red cells, because the clinical demand for these is low and expiry rates relatively high given the low population prevalence,” she said. “The hospitals work very hard to minimise expiries and are closely scrutinised by the jurisdictional health departments and the National Blood Authority.”
Professor Wood said that the whole community had a role to play in ensuring sustainable blood supplies.
“GPs can actively promote blood donation and raise awareness of the many products that come from blood donation, such as immunoglobulin,” she said. “Many people don’t realise that these products are made from blood because they’re not red and they come in a little vial.”
According to Australian Red Cross, one in three Australians will need blood in their lifetime, but only one in 30 donates.
The most common blood type from pathology samples in the latest study was O RhD+ (38.4%), followed by A RhD+ (32%) and B RhD+ (11.8%).
To donate blood, visit Lifeblood to find your nearest blood donor centre and book an appointment.
Also online first at mja.com.au
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